Early transition metal catalysts for olefin polymers by coordination polymerization are well-known, typically those are the traditional Ziegler-type catalysts based on Group 4 and 5 of the Periodic Table (IUPAC new nomenclature) and the newer metallocene catalysts based on Group 4-6 metals. However, specific late transition metal catalysts suitable for olefin polymerization had not offered the same levels of activity or molecular weight capability for olefin polymerization during the development of these catalyst systems and additional work was published addressing this lack.
In Johnson, Killian, and Brookhart, J. Am. Chem. Soc., 1995, 117, 6414 the reporters describe the use of Ni and Pd complexes for the solution homopolymerization of ethylene, propylene, and 1-hexene. The catalyst precursors are square-planar, M.sup.2+, d.sup.8, 16 electron complexes incorporating substituted, bidentate diimine ligands. The active coordination sites are occupied by either methyl or bromide ligands. Methyl ligand complexes were activated with H.sup.+ (OEt.sub.2).sub.2 [B(3,5-(CF.sub.3).sub.2 C.sub.6 H.sub.3).sub.4 ].sup.- and bromide ligand complexes were activated with methylalumoxane (MAO) or diethylaluminumchloride as cocatalysts. All examples are solution process examples, the illustrated process temperatures do not exceed 25.degree. C. Examples 6 and 7 illustrate a significant increase in branching and significant decreases in M.sub.n and T.sub.m (by differential scanning calorimetry) when the illustrated solution process temperature is raised from 0.degree. C. to 25.degree. C.
Homogeneous processes such as high temperature solution and high pressure, high temperature polymerization processes, such as those at 500 bar and above, have shown particular suitability with metallocene systems. These processes allow for the improved productivity that occurs with greater reactivities at high temperature, the high pressure maintaining an essentially single phase reaction medium while permitting the higher temperatures. See, U.S. Pat. No. 5,408,017 and its equivalent WO-A-93/05732, and EP-A1-0 612 768. In this last document, bridged and unbridged hafnium metallocene compounds stabilized by non-coordinating anions after activation with alkyl-aluminum are utilized in processes at temperatures exceeding 120.degree. C. These solution processes are preferably to be conducted at pressures of 500 to 3500 kg/cm.sup.2.
In view of the process advantages associated with high temperature processes, it is industrially desirable to identify conditions under which late transition metal olefin polymerization catalysts can be effectively utilized.